How do capacitors work?

Capacitors arose from the need to store electrical charges in order to use them flexibly in the future when there is resistance in their terminals. The capacitor is an electronic component capable of storing electrical charge when connected to a voltage source, the capacitor has two terminals for its polarization (the largest terminal is positive and the smallest is negative), inside the capacitor the terminals are connected by plates metallic, usually aluminum, separated by a dielectric material. This dielectric material can be made of several materials, such as ceramic, teflon, mica, porcelain, cellulose, similar and even air. Dielectric is the insulating material that is capable of becoming conductive when subjected to a certain electric field value,


The dielectric material used in the capacitor determines the best time for application of the capacitor. Capacitance is the amount of electrical charge that a capacitor is capable of storing. Capacitance is measured in Farad, whose abbreviation is F. Capacitance is determined by the dimensions of the plates, directly proportional to the area (the more charge, the more intense the electric field) and inversely proportional to the thickness of the dielectric (Because the electric field is inversely proportional to the area). Capacitance is given by: C = Q / V, where:

C = capacitance, measured in Farad (F).

Q = electrical charges, measured in Columb (C).

V = voltage, measured in Volt (V).

How the capacitor works

As stated before, the main characteristic of the capacitor is the accumulation of electrical charges in two plates that are separated by a dielectric material. They are very close to each other. As they are opposite charges, they attract each other, being stored on the surface of the plates closest to the dielectric insulator. Due to this attraction, an electric field is created between the plates, through the dielectric material of the capacitor. The energy that the capacitor stores come from the electric field created between the plates. It is, therefore, electrostatic field energy.


Electrostatics is the branch of physics that studies electrical charges when they are at rest, or in balance, they are not in motion. This state of the charges is called static electricity, if these charges are in motion, the name of that event would be electric current, and this event is called Dynamic Electricity.

When the capacitor is charging or discharging there is a variable electric current value. But, as there is a dielectric material between the capacitor plates, this energy is just one plate to another, thus being stored.

When the capacitor is fully charged (reached steady state), or fully discharged (it is open) there is no such flow of energy, as the charges are not in motion since to be electric current the charges must be in motion.

Capacitors application

There are variations in the capacitor models, to suit different uses. As stated earlier, the dielectric material influences the situation in which the capacitor will be used. They are devices easily found in electronic circuits, and other places such as, for example:

  • Sensors;
  • Oscillators;
  • Noise filters on energy signals;
  • Absorb peaks and fill valleys in electrical signals;
  • Frequency divider in audio systems;
  • Cargo storage and flash systems in photographic cameras;
  • Insets of transistors in DRAM memories;
  • As temporary batteries and automotive sound (mega capacitor);
  • High power laser (capacitor bank);
  • Radars (capacitor bank);
  • Particle accelerators (capacitor bank);
  • Radio tuners (variable capacitor);
  • At the start of electronic gate motors (starting capacitor);
  • In power supplies;

One of the main applications of capacitors is to separate the alternating and direct currents when they are presented simultaneously. In direct current (DC) the capacitor behaves like an Open Circuit, and in alternating current (AC) the capacitor behaves like a resistance.

The difference between the capacitor and the battery is that the capacitor is much simpler. The capacitor stores energy, while the battery produces energy through chemical processes and stores it. The capacitor is much faster in the process of discharging the accumulated energy, compared to batteries, in addition to being applied on occasions where the battery has no application, such as, for example, dividing frequencies and smoothing electrical signals.